Vehicle license plate monitoring is used in a wide variety of applications including traffic control, controlling access to supervised areas such as parking lots or time limited parking spaces, and identifying stolen vehicles.
License Plate Recognition (LPR) (also referred to as License Plate Reader herein) is an image-processing technology used to identify vehicles by their license plate numbers. As used herein, license plate and license plate number refer generally to the alphanumeric character string normally used on license plates. This technology is used in various security and traffic applications including location of stolen vehicles and access control. LPR technology assumes that all vehicles have their identity displayed externally and that no additional transponder is required to be installed on the car. An LPR system uses illumination, such as infrared and a camera to take the image of the front or rear of the vehicle. Image-processing software then analyzes the images and extracts the plate information. This data is used for enforcement, data collection, and in access control applications.
An LPR system normally contains at least one camera, an illumination source, a frame grabber, computer software and hardware, and a database. The illumination source is a controlled light that can brighten up the license plate, and allow both day and night operation. In most cases, the illumination source is infrared, which is invisible to the driver. The frame grabber is an interface board between the camera and the computer, allowing the software to read the image information. The computer is normally a personal computer or laptop running Windows, Linux, or other suitable operating system. The computer processor executes the LPR application that controls the system, reads the images, analyzes and identifies the plate, and interfaces with other applications and systems. The software includes the LPR application recognition package. The hardware includes various input/output boards that are used to interface to the external world, such as control boards and networking boards. The database stores recorded events and can be a local database or a central database. The data recorded includes the recognition results.
Vehicle license plates can be monitored using portable devices installed in vehicles (e.g., patrol cars); installed overhead on poles or traffic signals; or positioned in proximity to an area to be monitored, such as a highway, parking lot, parking lot entrance, a freeway on/off ramp, etc.